Personal, self-programming, short-range transceiver system

ABSTRACT

A method for establishing a communication link between a transmitter and a receiver for the purpose of relaying audio material derived from an existing source to a user desiring to remain unencumbered by the source apparatus comprises the steps of placing: the receiver unit into physical contact with the transmitter unit, powering up both transmitter and receiver units, and waiting for an indication of process completion before setting the receiver unit in place. The transmitter unit searches for a free rf communication channel, initiates transmission of user-chosen audio material over permitted broadcast bands, and programs the receiver unit with information allowing it to receive on the same channel. The receiver unit is lightweight, worn in the outer canal of the ear or on the head in the conventional manner. The entire programming and transmission process takes place automatically without further user intervention. This method allows multiple users in proximity to receive their individually chosen source material or to enjoy a common transmission.

TECHNICAL FIELD

[0001] The technical field of the invention is that of a consumerelectronics device based on wireless transmission of information. Therange of transmissions is purely local (i.e., short distances up tothirty meters, more or less) and designed to provide a personaltransmission channel from a nearby audio source such as a tape recorder,record player, compact-disk player, radio set, and so forth. Thetransmitter and receiver technology operate in the standardradio-frequency bands such as the US 88 Megahertz (MHz) to 108 MHz FMband or in the unregulated low-power bands where standard frequency- andphase-modulation techniques are employed or in the very-low frequencyband where pulse-modulation techniques are common.

BACKGROUND ART

[0002] The field of consumer audio electronics comprises a wide varietyof personal listening devices—from hand-held and wearable radios andcommunicators to potable devices for retrieving audio information storedin many forms such as cassette-tape media and compact-disk media ofvarious types. There also exist various earphone devices auxiliary to orintegral with many of these personal entertainment devices. The vastmajority of these personal listening or entertainment devices requirethat the sound storage and playback unit, i.e., the sound source thatproduces an electrical signal in the audio range, be carried along withthe user. A majority of these latter devices that are equipped withpersonal earphone units send an electrical signal from the playbackdevice to the earphone device via a cable or wire, potentiallyencumbering the user or providing an easily noticed indicator that theuser is engaged in some sort of entertainment activity via an audiosource. Of course, there are a large number of such commercial devices,ranging from those trade-marked to those fully patent-protected, thatare easily recognizable in the marketplace. It is to be noted that thefield of such devices, comprising the bulk of the prior art, is toolarge to enumerate in this document. The following discussion will berestricted to devices that are more clearly and particularly focused inthe field of the present invention.

[0003] A commonly encountered device is a fully functional FM or AMradio built into a set of wearable headphones. The advantages arecomplete portability, wearability, and tuneability over the fullbroadcast bands, including stereo reception for the FM band. For exampleU.S. Pat. No. 4,930,148 describes a headband radiophone containing areceiver-transmitter to reciprocally transmit or receive signals.Another example is furnished by U.S. Pat. No. 5,095,382 which describesa wireless headphone designed to reciprocally transmit and receivesignals by means of an infrared beam of light.

[0004] There are also several types of wireless headphones on the marketprimarily designed to allow the user to listen to audio sources such astelevision or a home-music or entertainment center without disturbingothers. The wireless nature of said devices allows the user freedom tomove about within the restricted range of the transmissions withoutbeing encumbered by wires or cables precisely as in the presentinvention. These wireless headsets are meant for use in restricted areasusually confined to a few rooms in or near a dwelling and do not providecapacity for a plurality of channels for multiple users. The lattercapability is achieved by purchasing multiple units. As each devicecomes with its own pre-assigned channel, these devices are not suitablefor group activities. The present invention would fulfill the statedpurposes of these existing devices yet not be burdened with theaforementioned restrictions and limitations. In particular, the presentinvention allows multiple independent users in the same proximity bymeans of its self-programming function, and it allows multiple users toshare in the same locally broadcast material without requiring multiplebase units or transmitters.

[0005] Closer to the present invention is U.S. Pat. No. 5,677,964, whichdescribes a transmitter-receiver system wherein the transmitter unit isinstalled in an audio equipment and the receiver unit is installed in anearphone. A goal here is to allow the user to listen to informationtransmitted from the audio equipment without interfering with others inthe vicinity or having exposed wires or cables between the audioequipment and the listener.

[0006] An invention likewise close to the present invention in the areaof miniaturization by describing a device fitting within the outer canalof the ear, is U.S. Pat. No. 5,734,976 which describes a micro-receiverfor receiving a high-frequency frequency- or phase-modulated signal andis based on single integrated circuits in BiCMOS technology integratingthe necessary amplifiers, oscillators, modulators, demodulators, filtersand audio amplifier.

[0007] The description of U.S. Pat. No. 5,677,964 includes a transmitterpartially fulfilling the role of the “base unit” described in thepresent invention. That of U.S. Pat. No. 5,734,976 is primarilyconcerned with a prosthetic hearing-aid device, yet certainly meets oneof the desired goals of the present invention in being small,lightweight, unobtrusive, and capable of being worn in the outer canalof the ear and containing the required receiver circuitry and powersupply. Neither of these descriptions considers a base unit thatautomatically selects the first available frequency band fortransmissions, or a base unit that automatically programs the receiverunit to receive transmissions on said frequency band, or a base unitthat is functionally as portable as the receiver unit. The seconddescription also implies that the associated transmitter unit is to beworn by the user as necessitated by utility of prosthetic hearing-aiddevices. Combining the essential ideas present in these two existinginventions approaches, but does not reach, the functionality andconvenience of the proposed invention.

DISCLOSURE OF INVENTION

[0008] The idea of the invention is to provide a private and unobtrusivemeans for a user to listen to a local (nearby) source of music or otheraudio entertainment or information on a dynamically selected channelthat is simple to establish and does not interfere with possibly manyother users at the same location. Logically and physically, theinvention comprises two distinct modules: (1) a receiver or earphone and(2) a transmitter or base unit It is thus the intention of the inventionto provide a wireless connection between the earphones and base unit,allowing the user to move freely about, unencumbered by cables or wires,within the limited range of the base unit's transmissions. It is aprimary intention of this invention to allow multiple users in the samelocation either to listen to independent sources of entertainment orinformation or, if desired, to share such sources with others possessingsimilar receiver units (earphones). Furthermore, it is the intention ofthe invention that the receiver unit be small, compact, lightweight, andunobtrusive both visually and kinesthetically.

[0009] The first module consists of a lightweight, wireless,radio-frequency receiver or receiver pair (for stereo sources) mountedin lightweight headphone or head set or earphones. “Earphones” in thefollowing description is understood to refer to any convenientear-external or internal device consistent with the contained receiverunits. The earphones may be either externally worn or internally fittedto be placed in the outer canal of the ear, as the user desires.Furthermore, the earphone receiver units are “self-programed” asdescribed below. This latter feature ensures simplicity of operation andease of use while maintaining flexibility of multiple devices operatingin the same local area while minimizing inter-unit interference.

[0010] The second module, the transmitter or base unit, has fourfunctions: (1) to select automatically a clear transmission channel forsaid transmission, (2) to program or lock the earphones to receiveexclusively on said automatically preselected channel, (3) to modulatean appropriate radio frequency on said channel by the chosen audio-levelinput for low-power transmission to the earphones, and (4) to providepower to the earphones by way of charging their contained batteries. Thebase unit is likewise small, lightweight, and portable, being just largeenough to contain (1) the scanning circuitry, (2) the programmingcircuitry, (3) the transmitter circuitry, (4) the battery-chargingcircuitry, (5) minimal controls and indicators, (6) appropriate signalconnectors, and (7) a battery or other type of power supply.

[0011] In a typical situation, the user switches both the earphones andthe base unit to the “on” position as indicated by small light-emittingdiode indicators and then inserts the earphones into specially designedreceptacles located in the base unit. The power-on action initiatescharging of the earphone batteries should they require it. This power-onaction also initiates a “scan” function comprising a sequence of eventsthat (1) effectively searches for an “open” channel, (2) locks afrequency synthesizer or phase-locked loop to the frequency of the firstopen channel thus located, and (3) sends a “lock” command via contactslocated in the receptacles to a frequency synthesizer or phase-lockedloop in each of the earphones. At the end of this “auto-programming”sequence, (4) a “ready” indicator or signal indicates that the user maynow remove the earphones and place them in position for listening,moving about the area as desired, within the limited range of thebase-unit's transmitter, receiving the audio information from the sourceconnected to the base unit via the standard process of demodulation,amplification, and presentation of the electrical signal thus obtainedto the earphones' electrical-acoustic transducers.

[0012] Other users of similar devices located within the sametransmission range, or even in overlapping transmission areas of thefirst device, will not find an open channel at the same frequency chosenby the unit just program or any active prior-activated units as well.Any base unit attempting to program its own earphones will scan for thefirst clear channel, starting at one end of the selected spectrum,ensuring that no user will interfere with any other and no strong,established broadcasts will interfere with a user's auto-selectedchannel. The number of channels available in any area depends on thebroadcast band chosen and the bandwidth (plus guard band) for eachdevice. As an example, assume parameters consistent with the standard USFM broadcast band of 88 to 108 MHz and 100 KHz bands, there would be“room” for perhaps 200 independent users, not accounting for any strongcommercial FM broadcasts, which would reduce this number by at least oneunit for each such strong station.

[0013] If other users of an identical device within the sametransmission range wished to listen on a common channel and hence to thesame audio source as provided via transmission by any given base unit,they would simply place their compatible earphones into the receptaclesof said base unit and depress a secondary “program” or “lock” controlbutton. Such action would lock their earphones to the preselectedchannel of the chosen unit. In this manner, multiple users can listen tothe same source, allowing for class or shared-listening activity.

[0014] Due to its compact nature, the earphone electronics arefabricated with surface-mount methods using standard integrated circuitsand monolithic lumped components. Discrete components are used in thecircuit where necessary to establish externally selected frequencyranges as well as other functions such as passive filters. Both receiverand transmitter units are separately powered, with the receiverearphones having a battery power supply, and the base unit either abattery or other means of power.

[0015] The key features of the invention are summarized as its abilityto avoid interference with commercial broadcasts due to the auto-scanfeature; to be compliant with communication authorities' rules of lowpower and short range in certain restricted bands; to its “foolproof”use based on minimal controls and no adjustments; to provide wirelessoperation; to contain rechargeable or replaceable batteries in baseunit; to contain rechargeable and/or replaceable batteries in earphones;to restrict the physical dimensions of the base unit into a small,compact, lightweight, and easily transportable and detachable moduleindependent from any particular source of program material; and toprovide the user with the earphones that are ultra-light weight and/orfit in outer ear or mounted on a lightweight, supporting frame.

[0016] Although the primary conception and purpose of this invention isto provide an auxiliary but extended capability for standard sources ofaudio material in the sense that any source device having the required“signal” or “audio” output connector with compatible impedancecharacteristics can be connected to the base unit described in thisinvention, there are numerous variations possible based on the describedinvention besides the mentioned uses of transmitting local audio tolisteners not wishing to be encumbered by wires or highly visible headpieces. These variations may be differentiated, among othercharacteristics, by various sources for the transmitted audio material.The preferred embodiment presented herein should in no way restrict thepresent invention to a particular configuration as regards usage.

[0017] A modification of the base unit could be made with a built-inmicrophone or an input with an impedance-matching amplifier and gaincontrol designed for such a microphone. Such a unit could be used tosend verbal messages or any other sound based on sound pressure waves tothose with compatible earphones. For example, a type ofselective-broadcast communication only to users having completed the“lock” process with the centrally chosen base unit could be established,allowing only those users to receive said communication, even though ina crowd or noisy location.

[0018] A modification of the base unit could be made to equip it with abuilt-in radio receiver allowing the user to select a local radiostation for listening remotely from said radio receiver. Otherwise andmore generally stated, the standard types of sound reproduction devicescould incorporate the invention described here rather than saidinvention serving said devices as an auxiliary. In which case, theauto-scanning and self-programming functions would be retained asessential to benefit from the innovations described herein.

BRIEF DESCRIPTION OF DRAWINGS

[0019]FIG. 1 depicts a particular representation of the base units andillustrates how the earphones fit into the provided receptacles.

[0020]FIG. 2 is a block diagram of a typical application illustratingthe logical relation of the audio source, base unit, earphones, and theuser following programming by the base unit.

[0021]FIG. 3 is a functional block diagram of the base unit showing thelogical relationships between the three functional modules of scanner,transmitter, and programmer.

[0022]FIG. 4 shows details of the functional modules comprising the baseunit depicted in FIG. 3.

[0023]FIG. 5 is a functional block diagram of one of the earphones; theother is identical except that it receives the alternate stereo channelwhen applicable.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] A transmitter-receiver system in accordance with the presentinvention is comprised of a transmitter unit (the “base unit”) that iseither a separate module connected to an audio source by means of acable or suitable connector or integral to such a source, and a receiverunit installed in an earphone or earphone pair (“earphones”). Theinventive arrangements are directed to methods and apparatuses forestablishing a clear channel for the desired transmission and forlocking the receiver units to said clear channel, ensuring that saidtransmitter and receiver units function together as an integratedsystem. Secondary goals of lightweight and unobtrusive earphones, themaintenance of sufficient energy for the earphones, and wirelesscommunications that includes modulation, demodulation, methods ofmaintaining frequency stability, amplification of rf and audio signals,and driving appropriate electro-acoustic transducers are accomplished byincorporating features and devices that are well known to those familiarin the art

[0025] The present invention has been accomplished to provide atransmitter-receiver system which eliminates the aforesaid problems andsimultaneously meets the particular objectives of effecting a privateand unobtrusive means of listening to a nearby source of information,said means being simple to use yet having minimal interference withother users of the same rf band in the same local area. To this end, awireless rf link between a self-programming, transmitting base unit, anda receiver mounted in small, lightweight earphones are described indetail. A particular preferred means for effecting these goals ispresented, along with obvious and useful variations that extend thepreferred means in several nonessential ways.

[0026] A power source, typically a battery, together with its necessaryconnections to each of the functional modules and devices depicted is tobe understood to be functionally present in all of the figures, as is asuitable return path (earth or ground) for returning current. to thepower source, thus completing the circuits as required.

[0027] Referring now to the drawings wherein like numbers refer to likeparts, FIG. 1 is a conceptual view showing the relationship between thebase unit 100 and the earphones 200 before and after the programmingoperation and schematically indicating the process of such programming.Other configurations are possible, so the illustration of thisparticular configuration is not to be restrictive for implementation oruse of the invention. A particular placement of the controls comprisingpower switch 102, indicator lights 104 and 106, and audio-inputconnector 108 are also shown. Control 112 allows manual programming ofthe earphones 200 once the programming operation is complete asindicated by indicator light 104 changing state from flashing to steady.The arrows indicate the process of inserting and removing the earphones200 from their programming receptacles 110 in base unit 100. Contacts201, 203, and 207, located on earphones 200, have mating contacts (notshown) in base unit 100 and allow communications necessary for theprogramming activity to take place between these two functional modules.

[0028]FIG. 2 is a block diagram showing the unified operation of theearphones 200 and the base unit 100. The earphones 200 have already beenprogrammed by the scanning function of the base unit 100 and are shownreceiving the rf signal modulated by the audio source, which may be anyof a plurality of readily available devices such as tape players,compact-disk players, and so forth. The presence of the user isindicated by a sketch of a head in the figure.

[0029]FIG. 3 is a block diagram of base unit 100 of FIG. 1. Theoperation of this unit is described in functional order starting withactivation of the power-on switch 102, which supplies power from battery118 to all associated electronics via line 111, resets all circuits andlogic in base unit 100 to a standard initial state, initiates thescanning and programming sequences, and causes the “scan” indicatorlight 104 to flash, indicating that the scanning sequence is in progressand that the unit has power. The function of the three submodules aredescribed here, while details are deferred to a subsequent figure.

[0030] The scanner 120 comprises a scan controller 130, a channeldetector 150, a shared frequency synthesizer 170, a transmit-receiveswitch 122 and indicator lights 104 and 106. Upon power-on, the scancontroller 130 examines the state of the earphones 200 via line 113; ifnot turned on before insertion into receptacles (110 of FIG. 1), warninglight 106 is illuminated indicating a procedural error to be corrected.The later criterion being met or the error corrected, the scancontroller 130 signals the programmer 190 via line 117 and starts afrequency-sweep sequence, sending coded information to the frequencysynthesizer 170 via line 119, controlling the frequency-scanningsequence. The channel detector 150 receives the synthesized frequency(local oscillator frequency) from line 121 via the switch 122, which isset to connect the frequency synthesizer 170 to the channel detector 150during the initialation sequence. The channel detector 150 then examinesthe signal from the antenna 114 via line 115 which signal is heterodynedwith the synthesized frequency entrant on line 121 in a manner familiarto those skilled in the art. The transmit-receive switch 116 is likewiseconfigured to connect the antenna to the channel detector 150 during theinitialization sequence. The function of the channel detector 150 is tolocate a frequency subband where there is little or no carrier present.Such a subband being located, the channel detector 150 signals the scancontroller 130 via line 123, whereupon scan controller 130 stopscommanding the frequency synthesizer 170 to advance, sends a signal tothe programmer 190 via line 125, changes the state of indicator light“scan” 104 from flashing to continuously on, indicating that the usermay proceed to the next stage. Additionally, switches 116 and 122 areset to the alternate or “transmit” state via signals (not shown) fromthe scan controller 130.

[0031] The programmer 190 comprises a battery charger 192 and a one-shotcircuit 194. Details concerning the action of the battery charger 192are known to those familiar with the art and are not elaborated uponhere. Upon receiving a start signal via line 117, the battery chargerexamines the voltage level on each of the batteries in the earphones 200(FIG. 1) and supplies any current needed to charge them to theoperational point, said charging operation taking place during the scansequence; the charging current is presented to the earphones via line127 through contact 103. Contact 107 made to each earphone via connectorblock or receptacle 110 transmits an enabling level from oneshot 194 vialine 129. Those skilled in the art recognize that oneshot 194 can bemade to emit a logic pulse of predetermined duration given a leading- ortrailing-edge trigger input as may be applied by the scan controller 130upon completion of its scan process or at the discretion of the user viaexternal control 112 via line 109. Contact 101 in connector block 110receives a sample of the frequency of the located rf subband via line124. Contact 105 in connector block 110 provides a common ground to theearphones.

[0032] The transmitter 160 comprises the shared frequency synthesizer170, a modulator 180, and an rf amplifier 162. At the end of the scancycle as indicated by signals from the scan controller 130, the switch122 is configured so that the signal from frequency synthesizer 170 isapplied as the carrier frequency to the modulator 180. The details ofthe phase and frequency modulation as performed by modulator 180 arewell known to those skilled in the art and need not be described indetail. The audio-in signal via connector 108 is used to modulate saidcarrier frequency, whence the modulated carrier is amplified asnecessary by rf amplifier 162 and allowed to reach antenna 114 throughswitch 116, which has changed state via a signal (not shown) from scancontroller 130.

[0033]FIG. 4a shows the details of the scan controller 130. Uponreceiving power via line 111 from the power-on switch (102 FIG. 3), ANDgate 134 senses the state of the unit's power. The state of earphones200 (FIG. 1) is sensed via line 113 by comparator 136 whose output,indicating “on” state for the earphones 200 (FIG. 1), is also applied toAND gate 134. Reference 132 in an internally set parameter chosenaccording to design parameters. The complementary state of thecomparator 136 is sent to buffer amplifier 138 which connects to “fault”indicator light 106 should the earphones 200 (FIG. 1) be in thepower-off state. The AND gate 134 passes the “start” logic levelobtained from the power line via line 111 when power is on in both thebase unit 100 (FIG. 1) and earphones 200 (FIG. 1). Power-on switch 102(FIG. 3), via line 111, also applies power (via the V_(CC) connectionscommon to all modules) to multivibrator 140 to send a flashing signal tobuffer 142 and thence to indicator light 104 indicating that a scan isin progress. The logic level from AND gate 134 triggers oneshot 144which emits a logic pulse or level of duration of approximately 1second, predetermined by the time-constant capacitor (not shown). Thislevel is applied to integrator 146 and thence to sample-and-follow 148.The output of sample-and-follow 148 follows the input from theintegrator 146 until it receives a “sample” command. Said output is sentto the frequency synthesizer 170 (FIG. 3) via line 119. Once a clearchannel is located as determined by the channel detector 150 (FIG. 3),line 123 is activated by said channel detector. A high logic level online 129, buffered by amplifier 149, causes sample-and-follow 148 tosample and transfer a digitally coded version of its input voltage toits internal digital memory, effectively maintaining said voltage levelfor subsequent presentation to the frequency synthesizer 170 (FIG. 3).The particular details of how said sample-and-follow accomplishes itsfunction are known to those familiar with the art. Said logic level online 129 also halts multivibrator 140, leaving it in a “high” state sothat indicator light 104 is now steadily illuminated indicating an endto the scan process and communicating the “ready” state to the user.

[0034] Referring now to FIG. 4b, which depicts the details of thechannel detector 150, an rf signal from the antenna 114 (FIG. 3) entersvia line 115 and is filtered in band-pass filter 151 which is set broadenough to encompass the frequency band of interest over which thetransmitted information might appear, depending on the particularoperating band pre-chosen for the device. Said signal thence passing torf amplifier 152 and to mixer 154 wherein said antenna signal isheterodyned with the frequency signal from frequency synthesizer 170(FIG. 3) via line 126 after being buffered by amplifier 153. Theheterodyned signal, now at baseband of the frequency from said frequencysynthesizer, is passed through low-pass filter 155. Filtered byintegrator 157 to remove ripples, the slowly varying, nearly DC signalis presented to comparator 158. Said comparator compares the inputsignal to a preset voltage reference level 159. When said signal fallsbelow a said reference value, the comparator communicates thisinformation as a voltage level via line 123.

[0035]FIG. 4c shows the details of the frequency synthesizer 170 whichcomprises a voltage-controlled oscillator 172 and a band-pass filter 174in this embodiment. Line 119 conveys the ramp signal produced byintegrator 146 (FIG. 4a) via sample-and-follow 148 (FIG. 4a), causingthe voltage-controlled oscillator 172 to slowly increase its frequencyfrom the lower end of the preselected frequency band to the upper end ofsaid band. Said increase in frequency is presented to the channeldetector 150 via lines 121 and 126 (FIG. 3) causing said channeldetector to scan the frequency band of interest until the input to saidvoltage-controlled oscillator no longer changes.

[0036] A block diagram of the earphone circuitry 200 is shown in FIG. 5.Said circuitry comprises a complete rf receiver system 220, thatreceives its signal to be selected and demodulated in the manner knownto those familiar with the art, via line 209. In the programming mode,which is controlled by the scan controller 130 (FIG. 3) via contact 207,the transmit-receive switch 210 connects contact 201 to the saidreceiver via line 209. Said transmit-receive switch is placed in theaforementioned position by powering up said earphones by closing switch204, which allows the internal battery 206 to be connected to the V_(CC)line that powers all modules present in said earphones. Once the baseunit 100 (FIG. 1) has selected an appropriate frequency fortransmissions, input to latch 208 rises via contact 207 having receiveda voltage level from one-shot 194 (FIG. 3) in programmer 190 (FIG. 3)via line 129 (FIG. 3). The falling edge of said voltage level triggerslatch 208 which commands switch 210 to disconnect line from contact 201and connect antenna 214 to receiver 220 via line 209. At this point, thereceiver is receiving and decoding the transmitted material encoded bythe transmitter 160 (FIG. 3). The decoded audio signal is presented toaudio amplifier 212 via line 211. Receiver 220 also produces anautomatic gain control signal in a manner familiar to those skilled inthe art, presenting said signal via line 213 to said audio amplifier forthe purpose of controlling the gain of said amplifier should the signalat the antenna 214 weaken or strengthen due to the user moving too farfrom or too close to the base unit 100 (FIG. 1). Followingamplification, the decoded audio signal is converted to sound-pressurewaves by the electro-acoustic transducer 215, whereupon the user maylisten to said audio signal while moving about the area.

[0037] In the preferred embodiment, receiver 220 is a simplephase-locked loop (PLL) well known to those skilled in the art. Said PLLis augmented in a manner likewise well known to provide a signalproportional to the strength of said carrier frequency for use as anautomatic gain control in addition to the demodulated frequency- orphase-modulated carrier that is subsequently amplified and converted tothe desired acoustic signal. The operation of said recover as regardsthe particulars of the present invention is described in the paragraphabove.

[0038] An alternate configuration that is more reliable in frequencylocking and holding, but requires additional circuitry, is brieflydescribed here. The alternate method relies on digital synthesis offrequency in the base unit 100 and communication of a digital code forsaid frequency to the earphones 200. This is accomplished by modifyingthe scan controller 130 as follows. Replace oneshot 144, integrator 146,and sample-and-hold 148 by an oscillator running at a rate ofapproximately 256 Hz and a monostable to produce a train of pulses thatare presented to digital frequency synthesizer 170 via line 119. Uponreceiving a pulse, said frequency synthesizer advances by approximately50 KHz more or less, presenting said frequency to the channel detector150, which functions as above. Upon selection of a suitable frequencyband, channel detector 150 signals scan controller 130 as above via line123. Said signal halts said oscillator, effectively maintaining thecurrent digital count held by the digital frequency synthesizer 170.Said digital frequency synthesizer is then clocked by a signal from scancontroller 130 via a line not shown to command said digital frequencysynthesizer to present the coded word locked in its internalscalar/counter as a parallel 8-bit digital word to a parallel-to-serialconverter in the scan controller 130. The serial code is subsequentlysent to contact 101 during the logic level strobe from said scancontroller via line 129. On the earphone side, via contact 201, theserial code is converted to a parallel digital 8-bit word by aserial-to-parallel converter (not shown) and read into the digitalfrequency synthesizer (not shown) contained as a part of receiver 220 ofsaid earphones 200.

INDUSTRIAL APPLICABILITY

[0039] The present invention is aimed at the consumer entertainment areawhere individual users desire privacy or wish not to disturb near-bypersons, desire freedom from constricting and unsightly wires, anddesire to be unencumbered by a the source of sound entertainment orinformation attached to their person. The invention is useful to anyonealready in possession of a primary sound source exemplified by but notrestricted to a cassette tape player, a commercial-band fm or am radio,a compact-disk player, a television set, or any form of local soundmonitor incorporating a microphone or other means of producingelectro-acoustic information or entertainment. As an add-on or auxiliarydevice to be used in conjunction with the aforementioned sound sources,possession of a device based on the present invention becomes adesirable goal. As a system incorporated into presently availableprimary sources of entertainment or information such as listed above byway of example, the present invention would materially extend thecapability of such primary sources and hence increase the usefulness ofsaid sources beyond that of said sources not incorporating the presentinvention.

[0040] Additionally, group activities such as museum tours wherein eachgroup member's earphones are tuned to the same base unit would also bean appropriate and desirable application. There are s systems currentlyavailable that meet this requirement, but once manufactured as aconsumer entertainment device, adaptation of the present invention togroup usage would be much more cost effective than such presentlyavailable systems. This group-usage functionality is incorporated intothe present invention by intention of design as described above.

[0041] By a simple modification, the receiver unit can be made topresent its audio signal to a connector rather than to acoustictransducers. Such signal being available as a source of information forself-powered speakers containing appropriate audio amplifiers. Thismodification allows, for example, a remote, indoor sound source toservice outdoor speakers, while maintaining the convenience of automaticchannel selection.

What is claimed is:
 1. A receiver unit or system comprising: a means forreceiving and demodulating frequency-, phase-, pulse-, oramplitude-modulated rf information; a means for decoding saidinformation to baseband to recover the encoded audio signal; a method ofgenerating and maintaining a local heterodyne frequency to accomplishsaid decoding; a method of selecting the source of rf input signal fromeither of two sources, said sources being an rf signal at from theintegral antenna or from an included input connector or contact; a meansfor converting said audio signal to an acoustic transducer; a means forincorporating the acoustic transducer within a earphone housing; and ameans for supplying necessary power to all circuitry.
 2. A base unit ortransmitter system comprising: a means for modulating a preselected rfcarrier frequency by an audio input signal, said means being eitherphase, frequency, pulse, or amplitude modulation; a means fortransmitting said modulated carrier; a method of selecting said carrierfrequency; a means for generating said carrier frequency by means of afrequency synthesizer, a means for monitoring and charging the earphonebatteries of claim 1; and a method of establishing the local heterodynefrequency of claim
 1. 3. The method of claim 2, wherein said selectionmethod subdivides the frequency band into a plurality of bands, one ofwhich, sufficiently free of interference, is chosen for transmission bythe apparatus of claim
 2. 4. An apparatus of claim 3 wherein saidsubdivision is accomplished by a swept, voltage-controlled oscillator,said sweep lasting a predetermined duration or until such time as asuitable channel has been located.
 5. An apparatus of claim 3 whereinsaid subdivision is accomplished by a digital frequency synthesizercommanded by incrementing a digital counter integral to said digitalfrequency synthesizer, said counter being incremented until a suitablechannel has been located.
 6. An apparatus of claim 3 wherein saidfrequency band is chosen based on the signal level present in aparticular bandwidth range said bandwidth range being selected by themethod of claim 3, the selected frequency being applied to a mixer thatmixes said selected frequency with the signal received by the antenna ofthe apparatus of claim
 2. The output of said mixer being filtered andcompared to a predetermined level. The criterion for selection of saidfrequency band being that said output be lower than said predeterminedlevel.
 7. A method of commanding or programming the apparatus of claim 1to cause said apparatus to start receiving on the frequency bandselected by the apparatus of claim
 2. 8. An apparatus of claim 7 forcausing a command signal from the apparatus of claim 2 to the apparatusof claim 1 and information describing the carrier frequency from theapparatus of claim 2 to the apparatus of claim 1 by means of a commoncontacts between said apparatuses, said command signal being a logiclevel and said descriptive information being a sample of the output ofthe carrier frequency generated by the frequency synthesizer of claim 2.9. An apparatus of claim 8, said command signal being a logic level ofsufficient duration and said descriptive information being a binary codedescribing said carrier frequency, the length of said descriptiveinformation presented to the apparatus of claim 1 being determined bythe duration of said logic level.
 10. A method of claim 9 wherein thelength of said descriptive information is determined by the trailingedge of said command signal logic level.
 11. An apparatus of claim 1wherein said local heterodyne frequency is maintained by a phase-lockedloop subsequent to transmission from the apparatus of claim 2established by the command level of claim
 8. 12. An apparatus of claim 1wherein said local heterodyne frequency is maintained by a digitallycontrolled frequency synthesizer that receives its code from theapparatus of claim
 9. 13. A method of claim 2 wherein any apparatus ofclaim 1 may be frequency locked to any representative apparatus of claim2 once said apparatus is transmitting.
 14. The apparatus of claim 1,wherein said electronics are manufactured with surface-mounttechnologies using monolithic integrated, discrete-component circuits,effecting a micro-receiver suitable for miniature earphones.
 15. Theapparatus of claim 2, wherein said audio source is contained within theapparatus of claim 2 rather than being an auxiliary or external source.16 The apparatus of claim 15, wherein said contained audio source is amicrophone with associated level control components.
 17. The apparatusof claim 2, wherein said apparatus is incorporated into or containedwithin other electronics devices that provide source material fortransmission.
 18. An apparatus of claim 1, wherein said electronics aredigital in nature, making use of any of the common digital methods ofdemodulation and decoding as customary in spread-spectrum devices, saidmethods being any of time-division multiple access, code-divisionmultiple access, or frequency-division multiple access.
 19. An apparatusof claim 2, wherein said electronics are digital in nature, making useof any of the common digital methods of modulation and encoding ascustomary in spread-spectrum devices, said methods being any oftime-division multiple access, code-division multiple access, orfrequency-division multiple access.
 20. The apparatus of claim 1,wherein said earphones are mounted externally to the ear and eitherattached to the ear by independent loop contrivances or attachedtogether with said attachment wire or frame being worn over the head inthe usual manner of earphones.
 21. An apparatus of claim 1, wherein saidreceiver unit presents its demodulated audio signal to a connectorrather than to an acoustic transducer, making said audio signalavailable for use by other electro-acoustic devices.